Heater for sealing flat-packs and the like



United States Patent Milton Stoll 14- 19 212th St., Bayside, N.Y. 11360 712,578

Feb. 15, 1968 Dec. 29, 1970 Continuation-impart of application Ser. No. 654,024, June 14, 1967, now Patent No. 4 ins,

lnventor Appl. No. Filed Patented HEATER FOR SEALING FLAT-PACKS AND THE LIKE 15 Claims, 7 Drawing Figs.

U.S. C1 219/462 l-l05b 3/00 Field of Search 219/535, 462, 521, 530, 531, 540,200, 553; 53/373(lnquired) References Cited UNITED STATES PATENTS 6/1905 Hadaway 338/254 2,932,718 4/1960 Marsters 219/530 2,796,914 6/1957 Park 219/553 3,009,304 11/1961 Swick 53/373 3,392,506 7/1968 l'laines 53/373 3,404,511 10/1968 Watts et a1 53/373 FOREIGN PATENTS 987,093 3/1965 Great Britain 28/62 1,135,561 12/1968 Great Britain 28/62 Primal E.raminer Bernard A. Gilheany Assistant Examiner-F. E. Bell AttorneyLackenbach & Lackenbach ABSTRACT: The sealing of electronic flat-packs is accomplished by a heater comprising a ribbonlike like heater. Heat is distributed by means of a high thermal conductivity pad. The package is heat-sinked in order to protect the enclosed circuitry from exposure to excessive temperatures. The heating pad is connected with a heat sink, to provide accurate positive temperature control and a controlled cooling profile. This heater is particularly adapted to feedback temperature control.

PATENTED UEC29 I875 SHEET 1 [IF 3 m u O T S N PATENTEUDEB29I9Y0 3.551.545

SHEET 2 OF 3 FIG 2 FIG 3 FIG 4 FIG 5 INVENTOR.

MILTON STOLL PATENTEUDECZQIQYB 3.551.645

SHEET 3 OF 3 FIG 7 MILTON STOLL IN VENTOR.

HEATER FOR SEALING FLAT-PACKS AND THE LIKE CROSS-REFERENCE TO RELATED APPLICATIONS Related applications include the application entitled Temperature Controller Employing Closed Loop Feedback and Incremental Programming filed 4, 3,502,706 bearing Ser. No. 642,627 and assigned to Group 345, and the application entitled Methods of and Means for Sealing Flat-Packs and the Like".frled June 14, 1967 and bearing Ser. No. 654,024, now U.S. Pat. No. 3,502,706 of which this application is a continuation-in-part. The entire disclosure of each of the aboveidentified copending applications are expressly incorporated herein, by reference,. as fully and completely as if fully reproduced herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is in the field of class 49, class and subclass 81, processes, uniting parts or class 81, tools, subclass 9.1 special sealing.

2. Description of the Prior Art No prior art references have been found.

SUMMARY The present invention provides a flatheating element which is closely coupled thermally to a high thermal conductivity heat transfer pad for heat-sealing flat-packs and the like. The pad has provisions for heat-monitoring as by a thermocouple and may be provided with a cover to prevent sticking to the package being sealed. Additional heat-sinking means is provided thermally coupled to the pad and its cover for thermally loading the pad so that decreasing as well as increasing temperatures can be sensitively and accurately controlled. Heatsinking means for the package is also provided in order to protect the enclosed electronic circuitry from exposure to excessive heating. A passage through the heater and pad permits connection to a vacuum system so that the cover to be sealed can be drawn against the pad facilitating loading of covers to be sealed. The heater of the present invention may be used to sealone package at a time or a plurality of packages may be sealed with the same heater.

BRIEF DESCRIPTION THE DRAWING FIG. 1 is exploded view of one form of the present invention.

FIG. 2 is an assembly view of the form of the invention shown in FIG. 1.

FIG. 3 is a detail of a portion of the device of the present invention.

FIG. 4 is a detail of one form of heating element suitable for use in the present invention.

FIG. 5 is a detail of another form of heating element suitable for use in the present invention.

FIG. 6 is a detail of a self-detaching interface shim suitable for use in the present invention.

FIG. 7- is a modification of the present invention which provides for sealing a plurality of flat packs with a single heater system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The heater for flat-pack sealing or the like is assembled from a series of parts shown in exploded form in FIG. 1. The elements include a ceramic base 1, ceramic spacers 2 and 3, heat sink holder 4, heat sink stem 5, upper pad 6 including a clearance hole 7 to pass the heat sink stem, upper insulator 8 also with a clearance hole 9, heater element 10, lower insulator 11 with clearance hole 12, heating pad 13 with clearance hole 14 and, an opening for a temperature transducer such as a thermocouple 15, heat pad cover 16 including socket 17 for attaching to heat sink stem 5, and heater element clamps 18 and 19. The whole assembly is put together with suitable bolts and nuts and includes suitable terminal studs, 20, 21, 22, 23,

24 and 25. The heating pad 13 is composed of high the thermal conductivity material such as silver or copper in order to provide an equi-temperature surface for sealing. The assembled heater is utilized to seal packages such as sealing cover 26 to package 27. In cases where cover 26 may tend to stick to heater pad 16, a thin npnsticking shim 28 may be placed therebetween. If this shim is made of material having a different temperature coefficient of expansion from both pad 16 and cover 28, it will be self-detaching upon cooling from the two upon cooling.

Since package 27 may contain heat sensitive devices such as semiconductor integrated circuits, the heater in accordance with the present invention provides protection for these circuits. This protection is possible since the heat is applied from above and the package during the heat-sealing operation rests on a heat sink 29 so that there is a steep temperature gradient from cover 26 to the bottom of package 27 where the circuits are generally located. Heat sink 29 sits in a socket 32 in socket block 31 which permits heat sink 29 to swivel and thereby to perfectlycover 26 against pad 16 even when the top and bottom of package 26-27 are not perfectly parallel. To insure this perfect alignment and intimate contact between cover '26 and pad 16 a pressure spring 33 is provided bearing against the bottom of socket block 31. Alignment may be additionally provided by seating the flange of block 31 against an alignment surface (see openings in plate 43 in FIG. 7 for example). The temperature gradient through thepackage being sealed can be controlled by proper selection of the material from which heat sink 29 is made. For example, a brass heat sink will conduct more heat from the package than a stainless steel heat sink and will hence create a greater temperature gradient in the package. Also local control of the gradient in the bottom of the package can be modified by means such as a relief opening 30 in the top surface of heat sink 29. Such a relief opening can be used to add a control to the effect of the heat sink on the temperature of the bottom of the package and hence the temperature gradient from heater to heat sink. A passage 42 through heat sink stem communicates with the surface of pad 13 and cover 16 so that when connected to a vacuum, system, the covers of flat-pads such as 26 can be held as a part of the loading operation. Still further control of the gradient can be achieved by a heat-insulating pad, not shown, placed between the bottom of the package and the heat sink 29.

FIG. 2 is an assembly view of the heater in accordance with the present invention. It will be apparent how this assembly goes together when taken in connection with the exploded view of FIG. 1.

FIG. 3 is a detail of the heater pad 13 showing how a thermocouple formed by joining leads 35 and 36 is placed in hole 15 as a part of the feedback control circuit.

FIG. 4 is a top view of one form of heating element 37 suitable for use in the heater of the present invention. This heating element is essentially a flat strip of heater material such as michrome bent along lines 34 to form a heater of the form shown by heater 10 of FIG. I. A central hole 38 is provided as a clearance hole to pass heat sink stud 5 without touching or shorting to it. This heater of FIG. 4 is a relatively low resistance heater. Higher resistance heaters may be provided in the forms shown in FIGS. 5 and 6 where slotting and cutting of the heater strips provide longer, higher resistance electrical current paths.

FIGS. 5 and 6 illustrate two forms of heating element in which the electrical current path has been elongated and its resistance increased. The ends 39 are broad and flat to provide good electrical contact with the electrical terminals. The heating element 41 provides a substantially equal constant width current path between the broad end terminals to provide increased resistance and equal heating without hot spots.

The central hole 40 is provided to clear the heat sink stem.

FIG. 7 illustrates a modification of the heater in accordance with the present invention which is also adapted for sealing a plurality of flat-packs simultaneously. The heater 51 is placed below the heat-diffusing pad 50. Both are made larger-while a platen 43 is provided with a plurality of openings 44 and 45 for passing corresponding heat sinks 47 and 46 to support a corresponding number of flat packs to be sealed. The flanges 48 on these heat sinks are pressed against the under sides of the openings by springs 42 so that the top surfaces of the heat sinks are level and accurately parallel with the top surface of platen 43. This insures simultaneous contact with all packages and all of the cover surface of the packages when brought in contact with heater 51. in this form of the invention the heater 51 is next to the packages to be sealed and the heat-diffusing pad 51 is on top. The temperature of the heater in this case is monitored by suitable means such as thermocouple 55 inserted in pad 50. 1

While only a few forms of the present invention have been shown and described, many modifications will b apparent to those skilled in the art and within the spirit and scope of the invention as set forth in particular in the appended claims I claim:

1. A heater for heating and/or sealing electronic circuit packages and the like constructed and arranged to enable rapid thermal energy transfer with such packages and temperature response to applied electrical signals so that the heating and/or sealing may be closely and finely regulated, programmed, contoured, profiled and controlled comprising, in combination:

a low mass electrical resistance heating element fabricated a of a flat strip to a laterally extensive substantially platelike configuration for providing a substantially uniform ther- 7 mal output over a substantial surface area while providing little storage of thermal energy and contoured to substantially conform to the surface contour of the package'area to be heated and/or sealed; and

thin heat-diffusing means of high thermal diffusivity thermally closely coupled-to said heating element extending substantially entirely across the surface thereof to further equalize the temperature profile thereacross and the normal or perpendicular heat transfer therefrom for rapid and efiicient conductive heat ftransferwith the package portion to beheated and/or sealed. v

2. A heater constructed and arranged to enable rapid thermal energy transfer with'a surface in contact therewith and temperature response to applied electrical signals so that the heating may be closely and finely regulated, programmed,

contoured, profiled and comprising, in combination, a low mass electrical resistance heating element fabricated of a flat strip to a laterally extensive substantially platelike configuration for providing a substantially uniform thermal output over a substantial surface area and contoured to substantially conform to the surface contour of the surface to be heated; thin heat-diffusing means of high diffusivity thermally closely coupled to said heating element extending substantially entirely thereacross to further equalize the temperature profile thereacross and the normal or perpendicular heat transfer therefrom for rapid and efficient conductive heat transfer with the surface to be heated; and means for supporting said heating elements and heat diffusing means for contact withsaid surface, said support means comprising controlled thermal diffusivity and being thermally closely coupled with said heating element and said heatdiffusing means for providing heat sinking thereof so that the temperaturethereof may closely follow a programmed changing temperature profile.

3. Heater defined in claim 2 whereinsaid support means comprises a thin, elongated stem of controlled thermal diffusivity with said heat diffusing means mounted therewith at one end portion thereof; p

4. Heater defined in claim 3 wherein said support comprises a tubular stem having a passage extending generally axially therethrough and provided with a generally radially extending flange adjacent said one end thereof and external screw threads extending from said flange to said one end, said heater strip having an aperture generally central thereof through which said screw threads are adapted to extend and said diffusing means being provided with a generally centrally disposed internally screw threaded aperture adapted to engage said external screw threads for mounting said diffusing means with said stem and clamping said heater means between said flange and said diffusing means so that said stem passage is exposed at the heat transfer surface. a

5. Heater defined in claim 4 wherein said stem is disposed substantially vertically and said heat-diffusing means is 'disposed' generally beneath said heater to define a heat transfer surface spaced apart fromsaid heater with the heat transfer surface of said heat-diffusing means extending generally horizontally across the lower end thereof in combination with a support platform disposed beneath said heatdiffusing means for supporting the surface to be heated there between and biasing means for urging said support platform generally upwardly towards said heat diffusing means for urging the surface to be heated into intimate conductive heat transfer relationship with said heat transfer surface.

6.,Heater defined in claim 5 particularly adapted for sealing of electronic circuit flat packages and the like wherein the surface to be heated comprises a flat cover thereof wherein said support platform comprises a heat sink adapted to engage the bottom of the package and a bearing block disposed beneath said heat sink, the'lower surface of said heat sink and the upper surface of said bearing block being provided with downwardly convex and upwardly concave curvalinear sur faces, respectively, enabling said'heatsink to swivel on said bearing block and thereby to perfectly align the package cover against the heat transfer surface even when thetop and bottom of the package are not perfectly parallel, the materials of said heat sink being selected for controlled diffusivity to enable the rate of heat transfer and thermal gradient downwardly through the package to be regulated and controlled.

7. Heater defined in claim 6 wherein said support heat sink comprises a material having high thermal diffusivity, to withdraw heat from the bottom of thepackage and thereby provide a maximum temperature gradient through said package during heating and/or sealing.

8. A heater for heating and/or sealing electronic circuit packages and the like constructed and arranged to enable rapid thermal and temperatureresponse to applied electrical signals so that the heating and/or sealing may be closely and finely regulated, programmed, contoured, profiled and controlled comprising, in combination, a low mass electrical revsistance heating element fabricated of a flat strip to a laterally package area to be heated and/or sealed; thin heat-diffusing means of high thermal diffusivity thermally closely coupled to said heating element extending substantially entirely across the surface thereof and adapted to provide an equi-temperature heat transfer surfacespaced apart from said heating element for rapidand efficient conductive heat transfer with the package portion to be heated and/or sealed; and a stem disposed substantially vertically with the heat transfer surface of said heat-diffusing means extending generally horizontally across the lower end thereof and further comprising a support platform disposed beneath said heat-diffusing means for supporting the package to be heated and/or sealed therebetween together with biasing means for urging said support platform generally upwardly towards said heat-difiusing means for urging the package portion to be heated and/or sealed into intimate conductive heat transfer relationship with said heat transfer surface.

9. Heater defined in claim 8 wherein said support platform comprises a heat sink adapted to engage the bottom of the I package and a bearing block disposed-beneath said heat sink,

the lower surface of said heat sink and the upper surface of said bearing block being provided with downwardly convex and upwardly concave curvalinear surfaces, respectively, enabling said heat sink to swivel on said bearing block and thereby to perfectly align the package cover against the heat transfer surface even when the top and bottom of the package are not perfectly parallel.

10. Heater defined in claim 9 wherein said support heat sink comprises a material having high thermal conductivity and diffusivity to withdraw heat from the bottom of the package and thereby provide a maximum temperature gradient through said package during heating and/or sealing.

11. Heater defined in claim 1 further comprising means for deadhering said heater from the package, said deadhering means comprising a differing coefficient of thermal expansion than the package.

12. Heater defined in claim 11 wherein said deadhering means comprises a sheet of material disposed, between said heat diffusing means and the package further comprising a different coefiicient of thermal expansion from said heat-diffusing means.

13. Heater defined in claim ll wherein said heating element comprises a substantially equal width path dual labyrinth.

14. Heater defined in claim 1 further comprising a thermo couple embedded within said heat-diffusing means.

15. Heater defined in claim 6 wherein said support heat sink comprises a spacer of low thermal diffusivity to limit the heat transfer outwardly from the bottom of the package and thereby reduce the temperature gradient through said package during heating and/or sealing 

